Scanning the .NET help files, help for the Convert.ToDateTime Method (Int64) returns the following information:

"This conversion is not supported..."

What's up with this?

Specifically, I am writing a VB.NET routine that is querying Active Directory. First of all, I can't understand why the following AD fields are of data type Long:
   badpasswordTime
   pwdlastset
   usncreated
   accountexpires
   lastlogoff
   usnchanged

...while the following fields are of data type Date:
   whencreated
   whenchanged

They should all be date-time values shouldn't they?

It wouldn't be a problem if the routine mentioned in the subject of this email were available, but it's not. How would one go about converting one of these 64-bit signed integer values to its equivalent DateTime format value (using VB.NET)?

Thanks in advance!